The present invention relates to an arrangement of at least one sensor on the landing gear of an aircraft for measuring the weight and position of the center of gravity of the aircraft.
In the arrangements of this type which are known from actual practice, there are provided, in particular, inductive sensors of the type having two series-connected coils which are arranged, one above the other, with a common center line in a first sensor part, and having a tongue of thermomagnetic material which is movable in the coils and is part of a second sensor part. The first and second sensor parts are arranged on respective lugs of a pair of lugs which protrude at the measurement point from an axle or a bogie beam of an aircraft landing gear. The series-connected coils of the sensor act as inductive voltage divider and give off a signal when the vertical position of the tongue is displaced with respect to the coils. In the ideal case, the sensor only measures the shear which is caused by the load introduced into the landing gear of the axle or of the bogie beam in the region of the measurement point on which the sensor is arranged.
The errors which cause the result of the measurement to deviate from the ideal case include an error which is due to the loading and unloading effect. It is based on the fact that upon the loading and unloading of an aircraft, the bending of the load bearing parts in the landing gears depends on whether or not the aircraft moved -- rolled -- after the loading or unloading. Before the loaded aircraft is moved, a load is introduced closer to an inner wheel bearing than to an outer wheel bearing due to the action of a lateral force which acts on the tires and attempts to broaden the track of the axle. After movement of the aircraft, the lateral force disappears due to the change in the frictional conditions with respect to the ground, which permit a change in track. The vertical introduction of load due to the weight then takes place centrally between the inner and outer wheel bearings.
In order to describe the error known as loading or unloading effect, one can view the above-described migration of the introduction of the load as breaking down into a fixed introduction of load centrally between the wheel bearings, and a variable bending moment or moment of rotation as a function of the change in track. These moments are introduced into the axle at the wheel bearings. In addition to a bending of the axle, the weight-induced fixed introduction of load causes a shear, which is to be measured. Corresponding to the shear, the sensor experiences a deflection which is proportional to the weight. The moment of rotation or bending moment produced by the loading or unloading causes an additional bending which superimposes itself on the bending from the fixed load introduction and does not come directly from the load but from the lateral force on the tire. In the case of the conical development of the axle which is customary in practice, its strength decreases from the middle outward towards the wheel. This has the result that the curvature of the bending line is less at an inner sensor attachment point, which is located close to the center point, than the curvature on the outer sensor attachment point since the axle has a higher strength further inward than it has on the outside. It may be noted at this point that the loading effect is dependent on the size of the load and increases with the latter. By loading, refueling of the aircraft is also understood.